In contrast to other types of printers, inkjet printers provide fast, high resolution, black-and-white and color printing on a wide variety of media, and at a relatively low cost. As a result, inkjet printers have become one of the most popular types of printers for both consumer and business applications. Inkjet printers deposit ink onto a sheet of media by ejecting tiny drops of ink from a printhead. The inkjet printhead includes a plurality of ink ejection mechanisms, essentially tiny nozzles, that are formed on a substrate. The substrate is connected to an ink supply to deliver ink to the ejection mechanisms. Each ink ejection mechanism includes a firing chamber with at least one ejection orifice and one or more firing resistors located in the firing chamber. Control circuitry, located on the substrate and/or remote from the substrate, supplies current to the firing resistors in selected firing chambers. The ink within the selected chambers is super-heated by the firing resistors, causing the ink in close proximity to the resistors to be vaporized. This forms a bubble that pushes ink through the chamber orifice toward the printing medium in the form of an ink droplet.
Due to the many processing steps required to create the various printhead structures on the substrate, the printhead is typically one of the most expensive parts of a printer. Furthermore, the cost of the printhead tends to increase with the size of the printhead. For smaller printers, the cost of the printhead may be low enough to allow use of an integrated ink supply system in which the printhead is permanently attached to the ink supply. Larger printers, however, often use a separate ink supply system, in which the printhead is a separate component from the ink supply. In this arrangement, the ink supply may be replaced without having to replace the printhead, thus significantly cutting the cost of new ink supplies. Nevertheless, the printhead may still require periodic replacement due to printhead failure.
One of the most common causes of printhead failure is the accumulation of excess air in the printhead. Air that accumulates in the printhead can expand with increases in temperature or altitude, causing ink to drool out of firing chambers. Air bubbles can also block small ink paths, causing the printhead to “deprime”. This air may come from several possible sources. For example, because the ink supply and printhead are typically removable parts, seals may exist where these parts meet the ink delivery system. Any imperfections in these seals may allow air to enter the ink, where it may either dissolve into the ink (degassed ink is typically used in inkjet printers) or migrate to the printhead without dissolving. Air dissolved in the ink may then be evolved in the printhead due to the elevated temperatures in the printhead caused by the firing chambers.
Sealant greases may be used to coat the seals to prevent air leakage, but such greases may contaminate the ink, and thus clog the printhead. Furthermore, in the process of removing and installing printheads and ink delivery system components, a user may accidentally contaminate the ink delivery system with grease from an exposed seal. This may clog the ink ejection mechanisms of the other printhead with the sealant grease, causing the printhead to fail.